The invention pertains to a heatable plate assembly particularly a sputter cathode having a plurality of target segments consisting of target portions bonded to backplates and mounted on a cathode body.
Cathode devices for use in coating systems are known. These cathode devices consist essentially of a sputter target, which is rigidly connected to a target backplate and eroded during the course of the cathodic atomization process. By means of mounting devices provided on the target backplate, the target backplate is held in position together with the sputter target on a mounting plate, which is designed as a cathode body and which is provided with a cooling device. The surface areas of conventional substrates to be coated by the sputtering technique can be as large as 400.times.300 mm.sup.2, which requires that the sputter cathode be of similar size.
A disadvantage of the known sputtering systems is that, when a new target must be installed after the old sputter target has been used up, for example, special tools such as lifters are required. Another disadvantage is that in some cases the sputter target cannot be replaced by a single person. In addition, large sputter targets, although desirable in themselves, suffer from the disadvantage that, during the sputtering process, the sputter target and the target backplate are heated by the energy from the plasma in the form of radiation and by the kinetic energy released by the ions which have been accelerated onto the target. The sputter target therefore expands as a function of the heat transferred from the target backplate to the cathode body and as a function of the design of the cooling device provided in the cathode body. As a result of this heating, both the sputter target itself and the target backplate (cathode body) expand. Because the sputter target is normally bonded to the cathode body, the sputter target and the target backplate must be made of metals with the same or similar coefficients of thermal expansion to prevent differences in the extent to which they change in length or area, as illustrated by the behavior of a bimetal strip. This sharply limits the choice of materials.